Here's why your argument fails. Disclaimer: The following video is an amv. Meaning I'm not to be held responsible if it's linkin park etc. It's your job to mute it.http://mx.youtube.com/watch?v=l8Dz83iQMvY
If you can find any video of avatar that has fights like that I'll actually start watching Avatar. Say what you want about naruto, but Naruto back in its glory days has some of the best fights period.
And if you disagree with my I'll defend my statement against the other shonens.
Bleach: Looks good and has a good art style but it lacks the frames that you would see in a Naruto fight. Most of the fights in Bleach are just boring sword clashes (where two guys are holding their swords against each other in a futile standoff).
DBZ: Has a lot of frames but most of the time they're either looping the animation or starring at each other.
One Piece: Has a lot of frames during some fights, but overall doesn't have enough fighting. I don't even see One piece as a shonen fight show. It's more adventure than fighting.
Yu Yu Hakusho: Has a good art style but Yu Yu Hakusho didn't age very well. Yu Yu's fights need to be re-done. The first three seasons of Yu yu was badly animated. The Dark Tournament on the other hand is fine.
Rurouni Kenshin: Is meh. With the exceptions of a few fights, Rurouni Kenshen's fights are average. Rurouni Kenshin had too much filler fights, and not enough serious fights.